Perfluorocyclobutane (c-318 or octafluorocyclobutane, b.p. -6.degree. C.) is a valuable material which can be used as a propellant, etch gas, and fire extinguishant. This compound is typically made by cyclodimerization of tetrafluoroethene (TFE) or is recovered as a co-product from the manufacture of TFE. As a result c-318 may be contaminated with unsaturates such as E- and Z-perfluoro-2-butene (i.e., CF.sub.3 CF.dbd.CFCF.sub.3 or PFC-1318my). These compounds are toxic and must be removed prior to commercial use. PFC-1318's are difficult to separate from c-318 by distillation as the boiling points are similar.
Saturated by-products are also typically produced during the c-318 manufacturing process. These include isomers of compounds of the formula C.sub.2 Cl.sub.2 F.sub.4, C.sub.2 HClF.sub.4 and C.sub.2 H.sub.2 F.sub.4. Some of these impurities form azeotropes with the c-318 and some have similar boiling points. Hence, separation of c-318 from saturated by-products can also be challenging.
U.S. Pat. No. 5,001,287 discloses a process for treating an impure mixture consisting essentially of at least one olefinic impurity and at least one saturated halocarbon by contacting the mixture with a source of hydrogen in the presence of a hydrogenation catalyst (e.g., a catalyst containing a Group VIII metal or rhenium). Perfluorocyclobutane is included among the examples of saturated halocarbons.
U.S. Pat. No. 5,763,698 discloses a process for reducing the fluorine content of hydrochlorofluorocarbons and hydrofluorocarbons by reacting these compounds with HCl in the vapor phase at an elevated temperature in the presence of a catalyst.
U.S. Pat. No. 5,345,017 discloses a process for reducing the fluorine content of acyclic fluorocarbons and chlorofluorocarbons by reacting these compounds with HCl in the vapor phase at an elevated temperature in the presence of a catalyst. In Example 8, a linear perfluorocarbon, perfluoropropane is converted to chlorofluoropropanes.
There is a need for alternative methods of purification.